Albedo-corrected parameterized equivalence constants for coarse-mesh nodal analysis of nuclear reactors

Abstract

This thesis introduces the albedo-corrected parameterized equivalence constants (APEC) method, a new method for correcting the homogenized two-group cross-sections of the PWR fuel assemblies by taking into account the neutron leakage. In order to eliminate the two-group constant error in the conventional homogenization method, the APEC method is proposed, which parameterizes the homogenized two-group cross-sections in terms of an integrated albedo information, current-to-flux ratio (CFR), and a neutron spectrum index defined as the fast-to-thermal flux ratio. Small color-set models are introduced to obtain appropriate CFR boundary conditions for the APEC method and their characteristic features are discussed. The APEC algorithm was implemented into an in-house nodal expansion method code in conjunction with a partial-current CMFD acceleration. The nodal analyses of various benchmark problems based on an SMR initial core and a large PWR core were performed to evaluate the performance of the APEC method. The nodal analyses showed that the APEC method can improve the nodal accuracy significantly with a marginally additional computing cost. In addition, the APEC method can be extended to the functionalization of the discontinuity factors (DFs) and it has been shown that APEC-corrected DFs results in clearly improved nodal solutions.